The present invention relates to the testing of the bonding of leads connecting a device to a frame or support ring. The most prevalent method of interconnect from the bonding pads of an IC device utilizes individual wire bonding techniques. Either thermocompression, thermosonic, or ultrasonic bonding is used to connect the usual gold or aluminum wire to the interconnect pad (bonding pad) of the IC device. Typical wire diameters used are 0.001" to 0.003". High reliability requirements as well as process monitoring checks induced the development of wire pull machines to insure viable wire to pad or wire to lead connections.
This is typically done using a fine wire hook that is positioned around the interconnect wire to be tested and pulled in a vertical direction as shown in FIG. 1. The amount of force required to pull the wire from the pad is measured for a destructive test, or a fixed force is applied in a non-destructive mode. In this case if the bond does not lift, it is acceptable. Most space flight applications requires 100% non-destructive pull testing. Wire pull testing is performed under 25X-50X magnification and is typically a tedious task due to the very small spaces in which the hook must be maneuvered. Each wire must be individually pulled, which is time consuming, and can occasionally result in damage to the wire under test, or to surrounding wires.
With the advent of Tape Automated Bonding (TAB) in the high reliability environment, there is a need for an alternate method of non-destructive lead pull testing. TAB bonding entails attaching the entire series of leads, in this case flat, wide, previously patterned, to the device at one time. Typical attachment methods are thermocompression bonding, and recently developed thermosonic single point bonding. The TAB process allows the bonding pads on the device to be moved closer together, a feature desired by device designers to reduce device size as shown in FIG. 2. At the same time, the flat leads occupy more of the space in a plane radiating from the die surface than do the individual round wires of wire bonding.
This makes the task of pulling individual TAB leads very difficult due to the geometries involved. The hook typically used cannot easily fit between the leads and subsequently damages surrounding leads, making non-destructive testing very difficult. Other mechanical methods, such as pushing on the lead from the bottom surface have been attempted with limited success. Performing a destructive pull test is possible with the hook, proceeding around the device in one direction. When a lead is pulled away, clearance is made for the subsequent lead as illustrated in FIG. 1.
Thus it is an object of the present invention to provide a method and apparatus for testing bonding of leads which does not require a pull hook.
It is another object of the present invention to provide a method and apparatus for testing bonding of leads which is capable of being used with tape automated bonded leads.
It is an even further object of the present invention to provide a method and apparatus for testing bonding of leads in large groups or all simultaneously.
It is still an even further object of the present invention to provide a method and apparatus of identifying how many or which leads fail a bond test when more than one lead is tested simultaneously.
These and other objects are achieved by applying a fluid force to a lead and determining if a lead separates at its bond in response to fluid force. The fluid force is applied to the bonding face of the lead. Where the device includes a plurality of leads, the fluid can be applied to all the leads simultaneously or to given groups of leads. The determination of how many and which leads are separated is produced.
To determined which and how many leads are separated in response to the force, a sensor is positioned adjacent the leads and an indicator is connected to the sensor to indicate if one or more leads contact the sensor or which leads contact the sensor. The sensor can be a conductor connected in circuit with an indicator and the circuit is closed by a lead contacting the conductor. The fluid pressure applied may be for destructive testing, wherein the fluid pressure is increased until a lead separates from its bond. This pressure at which it separates is an indication of bond strength. Alternatively, non-destructive testing can be conducted, wherein the fluid pressure is applied at a pressure sufficient to separate unacceptably bonded leads while not separating acceptably bonded leads.
Other objects, advantages and novel features of the present invention will become apparent from the following detailed description of the invention when considered in conjunction with the accompanying drawings.